The present invention relates to a combustion-type power tool, and more particularly, to a combustion-type fastener driving tool in which a combustible liquidized gas is ejected from a gas canister into a combustion chamber, mixed with air and ignited to drive a piston, thus generating power to drive fasteners such as nails or the like. The combustion type power tool is particularly used in the field of architecture and civil engineering.
A conventional combustion-type driving tool generally includes a housing, a handle, a trigger switch, a head cap, a head cover, a combustion chamber frame, a push lever, a cylinder, a piston, a driver blade, a motor, a fan, a gas canister, an ignition plug, an exhaust-gas check valve, a magazine, and a tail cover. The head cap closes one end of the housing through screws. The handle is fixed to the housing and is provided with the trigger switch. The combustion chamber frame is movable in the housing in the lengthwise direction thereof. The combustion chamber frame is urged in a direction away from the head cap by a spring, and one end of the combustion chamber frame is abuttble on the head cap against the biasing force of the spring. The head cover is attached to an upper side of the head cap through screws for supporting the motor in cooperation with the head cap and for protecting an upper end of the tool.
The push lever is movably provided at the other end of the housing and is coupled to the combustion chamber frame. The cylinder is secured to the housing and in communication with the combustion chamber frame. The cylinder guides the movement of the combustion chamber frame and is formed with an exhaust port. The piston is reciprocally movable in the cylinder and divides an interior of the cylinder into a lower cylinder chamber below the piston and an upper cylinder chamber above the piston. While the combustion chamber frame has its one end abutting on the head cap, a combustion chamber is defined in cooperation with the head cap, the combustion chamber frame and the upper cylinder chamber.
The driver blade extends from the end of the piston which faces away from the combustion chamber toward the other end of the housing. The motor is supported on the head cap. The fan is fastened to the motor and provided in the combustion chamber. The rotation of the fan by the motor mixes the combustible gas with air in the combustion chamber for promoting combustion. The fan also serves to introduce an external air into the housing when the combustion chamber frame is moved away from the head cap for scavenging within the combustion chamber frame, and at the same time serves to cool an outer peripheral side of the cylinder. The gas canister is assembleable in the housing and contains liquidized combustible gas such as propane and butane and a lubrication oil. The combustible gas is ejected into the combustion chamber through a gas passage formed in the head cap. The ignition plug is exposed to the combustion chamber for igniting a mixture of the combustible gas and air. The ignition plug includes a spark generating portion including a base electrode and an opposing electrode spaced away from the base electrode. The exhaust check valve is adapted for selectively closing the exhaust hole.
The magazine is positioned at the other end of the housing and contains fastening elements such as nails. The tail cover is interposed between the magazine and the push lever to supply the fastener from the magazine to a position of a moving locus of the driver bit. A guide clearance is formed at a lower end portion of the cylinder and the housing and at a portion where the driver blade passes for communicating the lower cylinder chamber with the atmosphere.
In order to provide a hermetic state of the combustion chamber when the combustion chamber frame is brought into abutment with the head cap, a first sealing member is provided at a predetermined position of the head cap for intimate contact with an upper portion of the combustion chamber frame and a second sealing member is provided at the outer peripheral surface of the cylinder near the head cap for intimate contact with a lower portion of the combustion chamber frame.
When the push lever is pushed against a workpiece, combustible gas is ejected into the combustion chamber from the gas canister assembled in the housing. In the combustion chamber, the combustible gas and air are stirred and mixed together by the fan. With this state, if the trigger switch is rendered ON, the ignition plug ignites the resultant mixture gas. The mixture gas explodes to drive piston for driving the driver blade, which in turn drives nails into a workpiece such as a wood block. After explosion, the combustion chamber frame is maintained in its abutting position to the head cap for a predetermined period of time. During this abutting period, the exhaust gas check valve is closed after the combustion gas is exhausted to maintain closing state of the combustion chamber. Further, thermal vacuum is generated in the upper cylinder chamber due to pressure drop caused by decrease in temperature. On the other hand, since the lower cylinder chamber is in fluid communication with the atmosphere through the guide clearance, the pressure in the lower cylinder chamber is greater than that in the upper cylinder chamber, so that the piston restores its original top dead center position. Thereafter, when the trigger switch is released and the push lever is moved to separate from the workpiece (not shown), the push lever is moved downward because of the biasing force of the spring to communicate the combustion chamber with the atmosphere, thereby performing scavenging by the rotation of the fan and recovering original position. See for example, U.S. Pat. No. 4,403,722.
As described above, in the conventional combustion type power tool, sealing by the sealing members are released in accordance with the rotation of the fan and the downward movement of the combustion chamber frame, so that exhaust gas after combustion is discharged to the atmosphere for cooling the combustion chamber. Accordingly, great amount of atmospheric air passes through the combustion chamber. In this case, such power tool is used under dusty working environment such as outdoor and building site where cutting wood chips and minute dust such as fibrous dust and soil dust are floating in the air. Such foreign materials are sucked into the power tool to cause operational breakdown. More specifically, lubrication oil contained in the combustible gas is adhered to various components of the power tool, and minute dust in the air is in contact with the lubrication oil and absorbed therein. Thus, the dust is deposited on the various parts of the power tool. Particularly, ignition cannot properly occur if greater amount of dust is deposited at a space between the base electrode and the opposing electrode of the spark generating portion. Consequently, combustion does not occur.
Other disadvantageous phenomenon is also noted on the deposition of the dust involved in the lubrication oil onto the annular grooves and O-rings serving as the first and second sealing members. By this dust deposition, upward and downward movement of the combustion chamber frame cannot be smoothly performed, making opening and closing of the combustion chamber difficult.
Conventionally, when such disadvantageous phenomena occur, several screws are unfastened to remove the head cap and the head cover from the housing to directly access the inner surface of the head cap and the combustion chamber frame. Thus, the base electrode and the opposing electrode can be subjected to cleaning with a cleaning liquid to remove the dust and lubrication oil therefrom, or first and second sealing members and ring grooves can be cleaned. Cleaning cycle is influenced by using environment of the power tool. If power tool is frequently used at the dusty environment, the cleaning must be performed by a weekly basis. Even if the power tool is used at a less dusty environment, cleaning must be performed by monthly basis. As described above, cleaning requires disassembly and assembly of the power tool, which prolong cleaning period. Further, parts and components such as screws may be missing and electrical wiring may be damaged as a result of disassembly.